I. Field of the Invention
This invention relates to a medical device useful in determining bleeding times, such as the time it takes for proper platelet aggregation to stop the free flow of blood, and more particularly, a single use, spring-loaded, disposable device for piercing the skin such as that of a human by employing a linear cutting edge transported by a moving carrier member in a direction substantially perpendicular to the skin to induce bleeding for carrying out bleeding time studies.
II. Description of the Prior Art
In the medical field it is a very common procedure, and often very necessary, to conduct a bleeding time test which measures the time required for the cessation of bleeding following a skin incision. This test is medically important because extended or prolonged bleeding time can be associated with, for example, a lack of or a great excess of platelets, abnormality of platelet function, coating of platelets by specific proteins or foreign materials or the action of certain drugs; e.g., aspirin.
Although the bleeding time test procedure was first described about seventy-five years ago, it did not receive general acceptance until the 1940's at which time the test's sensitivity was increased by making a skin incision on the forearm of the patient while maintaining a blood pressure cuff inflation of 40 mm Hg. Using this procedure, a technologist simultaneously starts a stop watch while making the incision. The emerging blood is then gently blotted every 30 seconds. The cessation of bleeding is defined as the time at which the blotting paper is no longer stained by the emerging board. This amount of time is generally recorded to the nearest half-minute.
U.S. Pat. No. 4,078,552 describes a prior art device that is used for making standard and reproducible skin punctures in a patient to determine bleeding time. The device comprises a housing, a spring-loaded blade shuttle, means for restraining the blade shuttle and means for irretrievable release of the blade shuttle to effect incision of the patient's skin through a slit opening in the housing. The direction of travel of the blade shuttle is perpendicular to the patient's skin and the cutting edge of the blade is described as linear.
The present invention is distinguished, in part, such as from the aforementioned U.S. Pat. No. 4,078,552, by the physical separation of the spring-loaded drive mechanism from the blade-shuttle, which is separately mounted and free to move totally independently therefrom. This separation enables implementation of the retraction feature described below.
On actuation, the spring transfers its stored energy to a first moving member, called the hammer, which then transfers its energy to the semi-freely mounted shuttle by a glancing percussive action, thereby imparting an energetic motion to the shuttle towards the skin, and especially the blade mounted thereon, which is guided in its tracks to exit the housing and inpact the skin. Following the percussive action, the hammer and shuttle are completely disengaged. The hammer travels to its final rest position to receive and lock a mating portion of the shuttle. The shuttle recoils to return into the housing from its exposed, incising position by a moderately-forceful, integral, leaf spring to latch that member in its locked or latched position. In this position, the shuttle and blade are safely latched out of the way of potential contact with any personnel, including the patient, thereby reducing opportunity for laceration or infection of medical personnel, visitors or other patients. Because the blade is latched up into the housing after use of the device, no special handling precautions need be used for safe disposal of the device.
The device described by the present invention has been measured by a "Ballistic Pendulum" type of device to be approximately 10 millijoules. The device described in U.S. Pat. No. 4,078,552 delivers about 1.7 millijoules. One reason that the device of the present invention must deliver more energy is that it does not have the luxury of relying on the restoration of the skin pressure against the blade to complete the incision process, as the device of the '552 patent does. The blade retracts so fast in the device of the present invention that it is effectively disengaged from the skin before the latter undergoes significant deformation. Furthermore, due to the design of the housing portion where the blade extends from the housing, the skin is stretched taut for easier penetration of the blade therethrough.
Conversely, the skin in the '552 device aids in the penetration of the blade since skin is hard and is tough to cut. The underlying tissue is spongy like gelatine and, under inward deformation, exerts a hydrostatic outward restoring force on the skin. Therefore, on the '552 device whose blade remains extended, the restoring force of the skin will continue the incision from the points of initial impact such at the blade ends. In the present device, because the blade moves through its cycle so quickly, it must rely totally on speed of penetration to complete the incision for the length of the cutting edge before the skin recoils from impact.
Another distinguishing feature over the '552 patent is the orientation of the blade on the shuttle such that, although the direction of travel is perpendicular to the skin, the cutting edge enters the skin at an angle of approximately five degrees from parallel. This makes for a unique slicing action caused by greater concentration of shear stress at the leading point of contact so that a lancet-type incision is made followed by extended shearing action as the blade edge penetrates to the position of maximum extension. The great speed of the present device also seems to be associated with reported reduction of sensation of pain. It is believed that the blade is retracted from the skin before nerve impulses can reach the brain.
Although the prior art does describe different types of devices for making skin incisions in a patient to determine bleeding time, none of these devices seem to have the combined advantage of reliability, ease of handling reproducibility, prevention of the formation of a scar in the patient, safety, speed of use, avoiding infection in the patient and minimizing pain to the patient.